An aircraft is propelled by several turbojet engines each housed in a nacelle which also houses an assembly of ancillary actuating devices related to the functioning thereof and ensuring various functions when the turbojet engine is or is not in operation. These ancillary actuating devices particularly comprise a mechanical thrust reverser system.
More precisely, a nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine, a downstream section housing the thrust reverser means and intended to surround the combustion chamber of the turbojet engine, and generally ends in an exhaust nozzle whose outlet lies downstream from the turbojet.
Modern nacelles are intended to house a turbofan jet engine capable, via the rotating fan blades, of generating a flow of hot air (also called the primary air stream) originating from the combustion chamber of the turbojet, and a flow of cold air (secondary air stream) also called the fan duct flow which circulates outside the turbojet through an annular bypass duct formed between a cowling of the jet engine and an inner wall of the nacelle. The two air streams are exhausted from the jet engine via the rear of the nacelle.
The role of a thrust reverser, on landing of an aircraft, is to improve the braking capacity thereof by re-directing forwardly at least part of the thrust generated by the turbojet engine. During this phase, the reverser blocks the bypass duct of the cold stream airflow and directs this stream towards the front of the nacelle, thereby generating a counter-thrust which adds to the braking of the aircraft's wheels.
The means applied to achieve this re-directing of the cold air stream vary according to the type of reverser. However, in all cases, the structure of the reverser comprises mobile cowls which can move firstly between a deployed position in which they open up a passage in the nacelle intended for passing of the diverted air flow, and secondly a stowed position in which they close this passageway. These cowls may fulfil a diverting function or simply an actuation function of other diverting means.
With regard to a thrust reverser known as a cascade reverser, the re-directing of the air stream is obtained via diverting vanes, the cowl merely having a sliding function intended to uncover or cover these vanes. Complementary blocker doors actuated by the sliding of the cowling, generally allow closure of the bypass duct downstream of the vanes so as to optimise the re-directing of the cold air stream.
These blocker doors are pivot-mounted at an upstream end on the sliding cowl between a stowed position in which, together with the said sliding cowl, they ensure the aerodynamic continuity of the inner wall of the nacelle, and a deployed position in which, in thrust reversing conditions, they come to close the bypass duct at least in part so as to divert a cold air stream towards the diverting vanes uncovered by the sliding of the sliding cowl.
The pivoting of the blocker doors is generally guided by links attached to the blocker door at a fixed point of the inner structure delimiting the annular bypass duct.
Yet since the guiding links pass through the bypass duct, they generate numerous aerodynamic perturbations in the secondary air stream.
Also, the fixing of these links on the inner structure requires the installation of fixed hinge points on the latter, which reduces the surface area of the inner structure which could be used for acoustic treatment of the said inner structure.
In addition, the thrust reverser structure is mechanically connected to the inner structure via the links. On this account, the thrust reverser structure and the inner structure are not independent of each other, which complicates dismounting thereof when maintenance operations on the nacelle or turbojet so require, in particular with external structures of so-called <<O-duct>> type i.e. manufactured in a single piece completely surrounding the turbojet, contrary to structures of so-called <<C-duct>> type comprising two semi-parts joined together around the turbojet.
To overcome these problems, numerous solutions have been proposed including the one described in patent application FR 2 907 512 to the Applicant.
In this application, a thrust reverser is proposed for a jet engine in which the sliding cowl is capable of translating by means of an actuating cylinder mounted on a fixed upstream structure. The actuating cylinder comprises a base housing a concentric driving slider having a terminal rod connected to the sliding cowl. The driving slider and the terminal rod are both mobile in a direction substantially parallel to the longitudinal axis of the nacelle independently of each other. The driving slider is also connected to a downstream end of the blocker door via a driving link so that a movement in translation of the slider is accompanied by pivoting of the link and hence of the blocker door, and in which actuation means are provided to drive the slider in translation when the sliding cowl is in a translation phase towards downstream.
However, a said thrust reverser is fairly complex to manufacture on industrial scale, and despite its advantages the implementation thereof entails some difficulties.
The link driving the blocker door may in particular pass through a monolithic skin called a diaphragm which blocks the passing of the cold air from the bypass duct to the vane when the sliding cowl is in stowed position. Yet, the purpose of the diaphragm is to ensure a simple, reliable sealed barrier against any outflow of cold air through the vanes in the closed position of the sliding cowl.
In addition, the seal between the bypass duct in which the cold air stream flows and the outside of the nacelle is formed on the external structure of the nacelle, inducing additional pressure on the inner structure of the nacelle. Therefore, it is necessary to reinforce this inner structure which penalises the weight of the nacelle.
Also, the actuating cylinder passes through the flow reversing vane preventing the installation of self-supporting vanes i.e. fixed radially onto each other to avoid the mounting of a carrier structure downstream of these vanes. A said self-supporting installation would allow savings in space and weight.
Additionally, since the end of the link is fixed onto the driving slider, this interferes with the reversing vane, reducing flow reversing efficiency and degrading the installation in the area of interference.